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Legumes and soybeans: overview of their nutritional profiles
and health effects.
Legumes play an important role in the traditional
diets of many regions throughout the world. In contrast in Western countries
beans tend to play only a minor dietary role despite the fact that they
are low in fat and are excellent sources of protein, dietary fiber, and
a variety of micronutrients and phytochemicals. Soybeans are unique among
the legumes because they are a concentrated source of isoflavones. Isoflavones
have weak estrogenic properties and the isoflavone genistein influences
signal transduction. Soyfoods and isoflavones have received considerable
attention for their potential role in preventing and treating cancer
and osteoporosis. The low breast cancer mortality rates in Asian countries
and the putative antiestrogenic effects of isoflavones have fueled speculation
that soyfood intake reduces breast cancer risk. The available epidemiologic
data are limited and only weakly supportive of this hypothesis, however,
particularly for postmenopausal breast cancer. The data suggesting that
soy or isoflavones may reduce the risk of prostate cancer are more encouraging.
The weak estrogenic effects of isoflavones and the similarity in chemical
structure between soybean isoflavones and the synthetic isoflavone ipriflavone,
which was shown to increase bone mineral density in postmenopausal women,
suggest that soy or isoflavones may reduce the risk of osteoporosis.
Rodent studies tend to support this hypothesis, as do the limited preliminary
data from humans. Given the nutrient profile and phytochemical contribution
of beans, nutritionists should make a concerted effort to encourage
the public to consume more beans in general and more soyfoods in particular.
Am J Clin Nutr . 1999 Sep;70(3 Suppl):439S-450S
Effect of genistein on in vitro and in vivo models of cancer.
In
two-thirds of studies on the effect of genistein-containing soy materials
in animal models of cancer, the risk of cancer (incidence, latency or
tumor number) was significantly reduced. In addition, purified genistein
delayed mammary tumor appearance in association with increased cell
differentiation in mammary tissue in rats treated with 7, 12-dimethylbenz[a]anthracene
when administered neonatally, inhibited phorbol ester-induced H2O2 production
in a model of skin cancer, and inhibited aberrant crypt formation in
a model of colonic cancer. In in vitro models, genistein inhibited the
proliferation of human tumor cell lines in culture with a wide variation
in IC50 values (2.6-79 mumol/L, or 1-30 micrograms/mL). In only a few
cases was the IC50 below 13.2 mumol/L (5 micrograms/mL), the presumed
upper limit for the serum genistein concentration in those on a high
soy diet. In future studies, greater emphasis should be placed on the
effect of genistein on nontransformed, normal cell lines from the tissues
where cancer can occur rather than established tumor cell lines. Similarly,
the effect of genistein on the progression and/or promotion of cancer
may be more clearly examined using nontransformed cell lines transfected
with specific oncogenes thought to be activated during oncogenesis.
J Nutr . 1995 Mar;125(3 Suppl):777S-783S
The effect of raloxifene on risk of breast cancer in postmenopausal
women: results from the MORE randomized trial. Multiple Outcomes of
Raloxifene Evaluation.
CONTEXT: Raloxifene hydrochloride
is a selective estrogen receptor modulator that has antiestrogenic
effects on breast and endometrial tissue and estrogenic effects on
bone, lipid metabolism, and blood clotting. OBJECTIVE: To determine
whether women taking raloxifene have a lower risk of invasive breast
cancer. DESIGN AND SETTING: The Multiple Outcomes of Raloxifene Evaluation
(MORE), a multicenter, randomized, double-blind trial, in which women
taking raloxifene or placebo were followed up for a median of 40 months
(SD, 3 years), from 1994 through 1998, at 180 clinical centers composed
of community settings and medical practices in 25 countries, mainly
in the United States and Europe. PARTICIPANTS: A total of 7,705 postmenopausal
women, younger than 81 (mean age, 66.5) years, with osteoporosis,
defined by the presence of vertebral fractures or a femoral neck or
spine T-score of at least 2.5 SDs below the mean for young healthy
women. Almost all participants (96%) were white. Women who had a history
of breast cancer or who were taking estrogen were excluded. INTERVENTION:
Raloxifene, 60 mg, 2 tablets daily; or raloxifene, 60 mg, 1 tablet
daily and 1 placebo tablet; or 2 placebo tablets. MAIN OUTCOME MEASURES:
New cases of breast cancer, confirmed by histopathology. Transvaginal
ultrasonography was used to assess the endometrial effects of raloxifene
in 1781 women. Deep vein thrombosis or pulmonary embolism were determined
by chart review. RESULTS: Thirteen cases of breast cancer were confirmed
among the 5,129 women assigned to raloxifene vs 27 among the 2,576
women assigned to placebo (relative risk [RR], 0.24; 95% confidence
interval [CI], 0.13-0.44; P<.001). To prevent 1 case of breast cancer,
126 women would need to be treated. Raloxifene decreased the risk of
estrogen receptor-positive breast cancer by 90% (RR, 0.10; 95% CI, 0.04-0.24),
but not estrogen receptor-negative invasive breast cancer (RR, 0.88;
95% CI, 0.26-3.0). Raloxifene increased the risk of venous thromboembolic
disease (RR, 3.1; 95% CI, 1.5-6.2), but did not increase the risk of
endometrial cancer (RR, 0.8; 95% CI, 0.2-2.7). CONCLUSION: Among postmenopausal
women with osteoporosis, the risk of invasive breast cancer was decreased
by 76% during 3 years of treatment with raloxifene.
JAMA . 1999 Jun 16;281(23):2189-97
Dietary effects on breast-cancer
risk in Singapore.
It
is suspected that diet influences the risk of getting breast cancer.
A study of diet and breast cancer was done among 200 Singapore Chinese
women with histologically confirmed disease and 420 matched controls.
A quantitative food-frequency questionnaire was used to assess intakes
of selected nutrients and foods 1 year before interview. Daily intakes
were computed and risk analysed after adjustment for concomitant risk
factors. In premenopausal women, high intakes of animal proteins and
red meat were associated with increased risk. Decreased risk was associated
with high intakes of polyunsaturated fatty acids (PUFA), beta-carotene,
soya proteins, total soya products, a high PUFA to saturated fatty acid
ratio, and a high proportion of soya to total protein. In multiple analysis,
the variables which were significant after adjustment for each other
were red meat (p less than 0.001) as a predisposing factor, and PUFA
(p = 0.02), beta-carotene (p = 0.003), and soya protein (p = 0.02) as
protective factors. The analysis of dietary variables in postmenopausal
women gave uniformly non-significant results. Our finding that soya
products may protect against breast cancer in younger women is of interest
since these foods are rich in phyto-oestrogens.
Lancet . 1991 May 18;337(8751):1197-200
Soy isoflavones--benefits and risks from nature's selective
estrogen receptor modulators (SERMs).
Phytoestrogens have
become one of the more topical areas of interest in clinical nutrition.
These non-nutrient bioactive compounds are ubiquitous to the plant
kingdom and possess a wide range of biological properties that contribute
to the many different health-related benefits reported for soy foods
and flaxseeds--two of the most abundant dietary sources of phytoestrogens.
Reviewed is the recent knowledge related to their pharmacokinetics
and clinical effects, focusing mainly on isoflavones that are found
in high concentrations in soy foods. Arguments are made for considering
soy isoflavones as natural selective estrogen receptor modulators
(SERMs) based upon recent data of their conformational binding to
estrogen receptors. Rebuttal is made to several key and important
issues related to the recent concerns about the safety of soy and
its constituent isoflavones. This article is not intended to be a
comprehensive review of the literature but merely highlight recent
research with key historical perspectives.
J Am Coll Nutr . 2001 Oct;20(5 Suppl):354S-362S; discussion
381S-383S
Phytoestrogen intake and endometrial cancer risk.
BACKGROUND:
The development of endometrial cancer is largely related to prolonged
exposure to unopposed estrogens. Phytoestrogens (i.e., weak estrogens
found in plant foods) may have antiestrogenic effects. We evaluated
the associations between dietary intake of seven specific compounds
representing three classes of phytoestrogens (isoflavones, coumestans,
and lignans) and the risk of endometrial cancer. METHODS: In a case-control
study from the greater San Francisco Bay Area, we collected dietary
information from 500 African American, Latina , and white women aged
35-79 years who were diagnosed with endometrial cancer between 1996
and 1999 and from 470 age- and ethnicity-matched control women identified
through random-digit dialing. Unconditional logistic regression analyses
were used to estimate odds ratios (ORs) and 95% confidence intervals
(CIs). RESULTS: Isoflavone (OR = 0.59, 95% CI = 0.37 to 0.93 for the
highest versus lowest quartile of exposure) and lignan (OR = 0.68, 95%
CI = 0.44 to 1.1) consumptions were inversely related to the risk of
endometrial cancer. These associations were slightly stronger in postmenopausal
women (OR = 0.44, 95% CI = 0.26 to 0.77 and OR = 0.57, 95% CI = 0.34
to 0.97 for isoflavones and lignans, respectively). Obese postmenopausal
women consuming relatively low amounts of phytoestrogens had the highest
risk of endometrial cancer (OR = 6.9, 95% CI = 3.3 to 14.5 compared
with non-obese postmenopausal women consuming relatively high amounts
of isoflavones); however, the interaction between obesity and phytoestrogen
intake was not statistically significant. CONCLUSION: Some phytoestrogenic
compounds, at the levels consumed in the typical American-style diet,
are associated with reduced risk of endometrial cancer.
J Natl Cancer Inst. 2003 Aug 6;95(15):1158-64 |